128 LOUIS PASTEUR 



with rare patience, determination, and energy. His 

 work on fermentation and spontaneous generation 

 with the many deceptive sources of error involved, 

 and his conquest of the diseases of wine had given 

 him a training in critical methods, in comparison 

 with which his ignorance of entomology was but a 

 trifling and easily remedied drawback. And yet in 

 this work Pasteur was destined to be deceived and 

 to labor on the basis of false hypotheses, but as he 

 put them to the test of crucial experiments, he 

 came finally out of darkness and confusion into 

 clearness and order. 



The disease in question had been introduced 

 about twenty years previously and had been 

 gradually becoming more widespread. It attacked 

 the worms in all stages of their development, some 

 dying before the first molt, or shedding of the 

 skin; others succumbed in later stages. Commonly 

 growth was checked, and the worms, ordinarily vora- 

 cious, would eat little or nothing. One common, 

 but not universal symptom was the appearance of 

 black spots upon the skin which resembled grains 

 of black pepper; this caused the disease to be 

 called pebrine. Often the afflicted worms would 

 begin a cocoon but would weaken and die before 

 it was completed. Others would spin normally, 



